<template>
    <ul class="list">
        <li class="item" v-for="item in letters" :key="item" :ref="item" @click="handleClick" @touchstart="handleTouchStart" @touchmove="handleTouchMove" @touchend="handleTouchEnd">{{item}}</li>
    </ul>
</template>

<script>
export default{
  name: 'CityAlphabet',
  props: {
    cities: Object
  },
  data () {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  computed: {
    letters () {
      const letters = []
      for (let t in this.cities) {
        letters.push(t)
      }
      return letters
    }
  },
  methods: {
    handleClick (e) {
      this.$emit('change', e.target.innerHTML)
    },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if (this.touchStatus) {
        if (this.timer) {
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() => {
          const touchY = e.touches[0].clientY - 79
          const index = Math.floor((touchY - this.startY) / 20)
          if (index >= 0 && index < this.letters.length) {
            this.$emit('change', this.letters[index])
          }
        }, 16)
      }
    },
    handleTouchEnd () {
      this.touchStatus = false
    }
  }
}
</script>

<style scoped lang="stylus">
@import '~styles/varibles.styl'
.list{
    position :absolute;
    top:1.58rem;
    right:0;
    bottom:0;
    width:.4rem;
    display:flex;
    flex-direction:column;
    justify-content :center;
    .item{
        line-height :.4rem;
        text-align :center;
        color:$bgColor
    }
}
</style>
